The present invention generally relates to the exchange of electronic data between a plurality of terminals and specifically to distributed multipoint conferencing.
According to the present industrywide accepted standard for multimedia conferencing over packetbased networks, i.e. the ITUT Recommendation H.323 (also termed H.323 standard for short) a distinction is made between differing types of multipoint conferencing, depending upon the way in which media streams are distributed, namely either centralized multipoint conferencing or distributed multipoint conferencing. The term xe2x80x9cmedia streamxe2x80x9d as used herein is intended to refer to audio streams, video streams, text streams, shared object streams (e.g. shared window streams), shared remote pointer streams and the like bit streams that are connected with conferencing.
In centralized multipoint conferencing all participating terminals send their media streams to a multipoint processor (MP) via unicast (pointtopoint) deliveries. The multipoint processor processes, (i.e. mixes or switches) all media streams received from the terminals and sends the resulting streams back to the terminals. In the case of audio media streams, signals sent from a terminal cannot be sent back to that source because of echo problems. That is one reason why MP implementations tend to be complex and expensive.
In distributed multipoint conferencing, on the other hand, all participating terminals send their media streams to all other participating terminals, and each terminal does its own mixing and/or switching of the media streams. Thus, there is no need for a multipoint processor. The terminals can send their media streams to the other terminals either via a multicast delivery (assuming that the network supports multicast) or via multiple unicast deliveries (multiunicast) if the network does not support multicasting.
In addition to these two methods, the H.323 standard specifies a hybrid-type multipoint conferencing in which the centralized approach applies to some media streams while the distributed approach applies to other streams. For example, audio streams are distributed directly to the terminals while video data streams are processed by a central video multipoint processor.
In addition to the specifications for media streams, the H.323 Recommendation also specifies the control architecture of a multipoint conference. Participating terminals communicate only via a multipoint controller (MC) which serves, inter alia, to invite and add new participants, to select the appropriate media codecs, to determine media distribution methods, and to inform the terminals of the addresses to be used for sending and receiving media streams.
When comparing the two multipoint conferencing methods just mentioned, the distributed approach has the advantage of not requiring an expensive MP. Furthermore, it scales well for large numbers of conferences because of its distributed structure. However, the number of participants within a conference is limited by the number of media streams which a terminal can process in parallel, and by the total network capacity consumed by the distribution of the media streams. The second limiting factor becomes critical when the network is accessed by a terminal via a low capacity link, and when multiunicast is to be used, e.g. because multicast is not supported by the network; this latter condition currently is the case with the majority of IPbased networks.
For a distributed multiunicast conference with N participating terminals, a terminal is required to send its media streams to the other (Nxe2x88x921) terminals and also to receive the streams sent by those (Nxe2x88x921) terminals. Consequently, the capacity required for a specific media by a terminal on its access link is B=2*(N1)*b, with b representing the capacity required by a single stream.
Assuming that a terminal accesses the network via a standard-type 28.8 kbit/s modem and G.723 is used for audio: with a G.723 audio stream consuming 6 kbit/s, such a terminal would be able to participate in an audio conference with only three parties.
Accordingly, a primary object of the present invention is to provide for a new distributed conferencing system and method capable of significantly reducing the link capacity required for one or more of the participating terminals.
This object and further advantages that will become apparent as this specification proceeds are achieved, in a first general embodiment of the present invention by a distributed multipoint conferencing system formed by a plurality of participating terminals for sending and receiving media streams in a conferencing interchange; the system further including at least one multipoint distributor (MD) connected to one of the terminals for receiving at least one or all of the media streams from that terminal but not from any other of the participating terminals; the multipoint distributor, on the other hand, is connected to the other participating terminals only for sending to them the media stream, or media streams, that it receives from its associated terminal; the other participating terminals receive additional media streams directly from any of the other participating terminals. In other words, any terminal that is associated with an MD, sends at least one or all of its media streams to the MD while it receives media streams either directly from the other terminals or from other MDs. By the same token, any terminal that is not associated with an MD in this manner sends its media streams directly, i.e. not via an MD, to all other terminals. Typically, up to ten terminals can participate in a conferencing system according to the invention and one, or more, or all of the terminals, can be associated with an MD of their own. As a matter of practice, an MD could be implemented in any general-purpose computer that includes a networking sub-system.
According to a preferred embodiment of the invention, the system includes high capacity linked terminals (HCL-terminals) mutually interconnected for sending and receiving media streams while the at least one terminal that is connected with the multipoint distributor is a low capacity linked terminal (LCL-terminal). However, connection of the multipoint distributor to an LCL-terminal is not a critical requirement. On the other hand, a conferencing system according to the invention may include more than one multipoint distributor in which case each multipoint distributor receives at least one media stream from its associated terminal; by the same token, all terminals of the system could be connected to, or supplied with, an associated multipoint distributor.
According to a further embodiment, the present invention provides for a distributed multipoint conferencing method between a plurality of participating terminals for sending and receiving media streams in a conferencing interchange; the method further including providing at least one multipoint distributor connected to one of the terminals for receiving at least one media stream from its associated terminal but not from any other of the participating terminals; the multipoint distributor being connected to the other participating terminals for sending to them the media stream or media streams received from its MD-associated terminal. The other participating terminals may also receive additional media streams directly from any of the other participating terminals.
Again, the conferencing method according to the invention may include one or more HCL-terminals and one or more LCL-terminals, wherein any LCL terminal is associated with its multipoint distributor.